Messages in this thread Patch in this message | | | From | Chengming Zhou <> | Subject | [PATCH v5 1/2] sched/core: Minor optimize ttwu_runnable() | Date | Thu, 8 Dec 2022 11:20:06 +0800 |
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ttwu_runnable() is used as a fast wakeup path when the wakee task is running on CPU or runnable on RQ, in both cases we can just set its state to TASK_RUNNING to prevent a sleep.
If the wakee task is on_cpu running, we don't need to update_rq_clock() or check_preempt_curr().
But if the wakee task is on_rq && !on_cpu (e.g. an IRQ hit before the task got to schedule() and the task been preempted), we should check_preempt_curr() to see if it can preempt the current running.
This also removes the class->task_woken() callback from ttwu_runnable(), which wasn't required per the RT/DL implementations: any required push operation would have been queued during class->set_next_task() when p got preempted.
ttwu_runnable() also loses the update to rq->idle_stamp, as by definition the rq cannot be idle in this scenario.
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> Suggested-by: Valentin Schneider <vschneid@redhat.com> Suggested-by: Peter Zijlstra <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> --- v5: - Split the reorganization and optimization into two patches per Chen Yu. Thanks!
v4: - s/This patch reorg/Reorganize/ per Bagas Sanjaya. Thanks!
v3: - Improve the changelog per Valentin Schneider. Thanks!
v2: - keep check_preempt_curr() for on_rq && !on_cpu case in ttwu_runnable(), per Valentin Schneider. - reorg ttwu_do_wakeup() and ttwu_do_activate() code, so ttwu_do_wakeup() can be reused in ttwu_runnable(), per Peter Zijlstra. - reuse ttwu_do_wakeup() in try_to_wake_up() (p == current) fast path too, so ttwu_do_wakeup() become the only place we mark task runnable. --- kernel/sched/core.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 314c2c0219d9..60aa7774e5f4 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3718,9 +3718,16 @@ static int ttwu_runnable(struct task_struct *p, int wake_flags) rq = __task_rq_lock(p, &rf); if (task_on_rq_queued(p)) { - /* check_preempt_curr() may use rq clock */ - update_rq_clock(rq); - ttwu_do_wakeup(rq, p, wake_flags, &rf); + if (!task_on_cpu(rq, p)) { + /* + * When on_rq && !on_cpu the task is preempted, see if + * it should preempt whatever is current there now. + */ + update_rq_clock(rq); + check_preempt_curr(rq, p, wake_flags); + } + WRITE_ONCE(p->__state, TASK_RUNNING); + trace_sched_wakeup(p); ret = 1; } __task_rq_unlock(rq, &rf); -- 2.37.2
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